The present invention relates to printing and bookbinding systems and, more particularly, to a paper sheet and signature feeder for such systems.
Various types of sheet and signature feeders are utilized in the printing and bookbinding industry. The term "sheet" or "paper unit" as used herein will be understood to mean "signature" or other combinations of folded or bound paper. A typical sheet feeder for low speed, low gloss paper is a single sheet friction drive having a top load tray and at least one feed roller which presses downward on a stack of paper in the tray. The feed roller is motor driven so that its rotation is effective to slide a single sheet of paper off the stack. Since this is a top-load, top-feed, the machine is stopped for reloading. Further, the rollers work well on single sheets of standard copy or bond paper but not as well on high-gloss print stock or folded paper.
Most other sheet and signature feeders use some form of vacuum assist to pick or pull sheets from a stack. One common high speed system uses a top feed vacuum system for picking up the top sheet on a stack and works well for all types of paper but not well on folded signatures which tend to unfold when lifted. Further, because of the way that signatures are prepared in the printing industry, the stacked paper is not level requiring automatic adjustment of the vacuum feed system.
A more elaborate system uses a combination of vacuum and grasping fingers to pull sheets from the bottom of a stack. In this system, vacuum devices grasp a bottom-most sheet or signature in a stack and slides the sheet into position to be grasped at an edge by grippers attached to a rotating drum which then slide the sheet from the bottom of the stack and deposits the sheet on a conveyor. This system works well on folded sheets when fed with the fold or spine edge towards the fingers. However, it does have difficulty with reverse fed (leading open end) signatures or other multi-page documents as well as single sheets.